Granular cold water swelling starches are well known. These starches can be prepared by suspending wet native starch granules in rapidly moving hot air and subsequently decreasing humidity (U.S. Pat. No. 4,280,851). Alternatively, they can be prepared by heating starch in an excess of water/alcohol with subsequent removal of liquid (U.S. Pat. No. 4,465,702).
When known granular cold water swelling starches are placed in hot or cold water, the granules swell excessively and release starch solubles into the aqueous phase. Upon drying, the individual swollen starch granules collapse and fuse together. Fused granules can be reground, but do not thereafter thicken efficiently and produce a dull taste in food products.
As a consequence of these properties, typical cold water swelling starches have only limited utility in food systems where gelling is to be avoided, e.g., in broths or other watery foods. In such watery systems, the conventional starches swell and gelatinize and release amylose, and upon storage give the food an unappealing texture. In addition, the fact that the known starches are not reversibly swellable (i.e., they are incapable of undergoing successive swelling/drying cycles) limits the utility of conventional starches.
U.S. Pat. No. 6,299,907 describes cross-linked, reversibly swellable granular starches. This type of starch is supplied by MGP Ingredients Inc. of Atchison, Kans. under the name SRS. The starches have a number of novel properties, including the ability to undergo multiple cycles of swelling in hot or cold water and drying while substantially retaining the individuality of starch granules and leaching minimal amounts of starch solubles.
Several attempts have been made to combine starches with minerals for various applications. In general, neutral carbohydrates, such as cellulose or native starch, form weak associations with ions and are regarded as having a poor chelating or metal interaction capacity (Kweon et al 2001, Hood et al 1977). On the other hand, mono-starch phosphate and distarch phosphate ester groups, which are commonly present in phosphorylated cross-linked starch, seem to play an important role in electrostatic attraction of ions in ion exchange absorption using granular starch. Mono- and di-starch phosphate groups provide a strong affinity for metal ions; however, traditionally cross-linked starches (e.g., starches cross-linked in the absence of pre-swelling) bind minerals on their surface. The limited void space in traditionally cross-linked starches makes the acceptance of minerals or ions into the intragranular region difficult.
Islam et al. (1992, 1998) compared native and hydroxypropylated rice starch treated with calcium carbonate. The level of calcium bound to the starch was in the range of 1-116 ppm.
U.S. Pat. No. 4,689,228 discloses a food supplement composition which contains a complex carbohydrate having a molecular weight in a range of from about 750 to about 3500 and a mineral.
U.S. Pat. No. 5,858,993 describes starch-metal complexes useful for accelerating the healing of topical wounds or as hair growth stimulants. The complexes described are prepared from native starch granules which are first solubilized to form a paste and then reacted with relatively high concentrations of copper (II) or tin (II) salts.
U.S. Pat. No. 2,801,242 discloses a method of making cross-linked starches mixed with inorganic flow agents to improve dry flow properties. The residual level of metal was less than 0.1% (starch basis).
U.S. Pat. No. 3,979,286 discloses a composition of cross-linked starch xanthate for removal of heavy metal ions from aqueous solution. Starch is first cross-linked and subsequently xanthated. The water soluble cross-linked starch xanthate reacts with polyvalent metal ions to form water insoluble precipitates, which can be effectively removed from aqueous solution by filtration.
U.S. Pat. No. 2,992,215 discloses a method of making chemically modified starch products useful for ion exchange chromatography. The products retain the original granular starch structure and are prepared by cross-linking the native granular starch with formaldehyde, followed by carboxymethylation or the attachment of 2-(diethylamino)ethyl groups. The ethyl groups are attached by ether linkages or other suitable means of attaching ionic groups to starch molecules.